//
// detail/strand_executor_service.hpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2022 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef ASIO_DETAIL_STRAND_EXECUTOR_SERVICE_HPP
#define ASIO_DETAIL_STRAND_EXECUTOR_SERVICE_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include "asio/detail/config.hpp"
#include "asio/detail/atomic_count.hpp"
#include "asio/detail/executor_op.hpp"
#include "asio/detail/memory.hpp"
#include "asio/detail/mutex.hpp"
#include "asio/detail/op_queue.hpp"
#include "asio/detail/scheduler_operation.hpp"
#include "asio/detail/scoped_ptr.hpp"
#include "asio/detail/type_traits.hpp"
#include "asio/execution.hpp"
#include "asio/execution_context.hpp"

#include "asio/detail/push_options.hpp"

namespace asio {
    namespace detail {

// Default service implementation for a strand.
        class strand_executor_service
                : public execution_context_service_base<strand_executor_service> {
        public:
            // The underlying implementation of a strand.
            class strand_impl {
            public:
                ASIO_DECL ~strand_impl();

            private:
                friend class strand_executor_service;

                // Mutex to protect access to internal data.
                mutex *mutex_;

                // Indicates whether the strand is currently "locked" by a handler. This
                // means that there is a handler upcall in progress, or that the strand
                // itself has been scheduled in order to invoke some pending handlers.
                bool locked_;

                // Indicates that the strand has been shut down and will accept no further
                // handlers.
                bool shutdown_;

                // The handlers that are waiting on the strand but should not be run until
                // after the next time the strand is scheduled. This queue must only be
                // modified while the mutex is locked.
                op_queue <scheduler_operation> waiting_queue_;

                // The handlers that are ready to be run. Logically speaking, these are the
                // handlers that hold the strand's lock. The ready queue is only modified
                // from within the strand and so may be accessed without locking the mutex.
                op_queue <scheduler_operation> ready_queue_;

                // Pointers to adjacent handle implementations in linked list.
                strand_impl *next_;
                strand_impl *prev_;

                // The strand service in where the implementation is held.
                strand_executor_service *service_;
            };

            typedef shared_ptr <strand_impl> implementation_type;

            // Construct a new strand service for the specified context.
            ASIO_DECL explicit strand_executor_service(execution_context &context);

            // Destroy all user-defined handler objects owned by the service.
            ASIO_DECL void shutdown();

            // Create a new strand_executor implementation.
            ASIO_DECL implementation_type

            create_implementation();

            // Request invocation of the given function.
            template<typename Executor, typename Function>
            static void execute(const implementation_type &impl, Executor &ex,
                                ASIO_MOVE_ARG(Function) function,
                                typename enable_if<
                                        can_query < Executor, execution::allocator_t < void>

            >::value
            >::type* = 0);

            // Request invocation of the given function.
            template<typename Executor, typename Function>
            static void execute(const implementation_type &impl, Executor &ex,
                                ASIO_MOVE_ARG(Function) function,
                                typename enable_if<
                                        !can_query < Executor, execution::allocator_t < void>

            >::value
            >::type* = 0);

            // Request invocation of the given function.
            template<typename Executor, typename Function, typename Allocator>
            static void dispatch(const implementation_type &impl, Executor &ex,
                                 ASIO_MOVE_ARG(Function) function, const Allocator &a);

            // Request invocation of the given function and return immediately.
            template<typename Executor, typename Function, typename Allocator>
            static void post(const implementation_type &impl, Executor &ex,
                             ASIO_MOVE_ARG(Function) function, const Allocator &a);

            // Request invocation of the given function and return immediately.
            template<typename Executor, typename Function, typename Allocator>
            static void defer(const implementation_type &impl, Executor &ex,
                              ASIO_MOVE_ARG(Function) function, const Allocator &a);

            // Determine whether the strand is running in the current thread.
            ASIO_DECL static bool running_in_this_thread(
                    const implementation_type &impl);

        private:
            friend class strand_impl;

            template<typename F, typename Allocator>
            class allocator_binder;

            template<typename Executor, typename = void>
            class invoker;

            // Adds a function to the strand. Returns true if it acquires the lock.
            ASIO_DECL static bool enqueue(const implementation_type &impl,
                                          scheduler_operation *op);

            // Transfers waiting handlers to the ready queue. Returns true if one or more
            // handlers were transferred.
            ASIO_DECL static bool push_waiting_to_ready(implementation_type &impl);

            // Invokes all ready-to-run handlers.
            ASIO_DECL static void run_ready_handlers(implementation_type &impl);

            // Helper function to request invocation of the given function.
            template<typename Executor, typename Function, typename Allocator>
            static void do_execute(const implementation_type &impl, Executor &ex,
                                   ASIO_MOVE_ARG(Function) function, const Allocator &a);

            // Mutex to protect access to the service-wide state.
            mutex mutex_;

            // Number of mutexes shared between all strand objects.
            enum {
                num_mutexes = 193
            };

            // Pool of mutexes.
            scoped_ptr <mutex> mutexes_[num_mutexes];

            // Extra value used when hashing to prevent recycled memory locations from
            // getting the same mutex.
            std::size_t salt_;

            // The head of a linked list of all implementations.
            strand_impl *impl_list_;
        };

    } // namespace detail
} // namespace asio

#include "asio/detail/pop_options.hpp"

#include "asio/detail/impl/strand_executor_service.hpp"

#if defined(ASIO_HEADER_ONLY)
# include "asio/detail/impl/strand_executor_service.ipp"
#endif // defined(ASIO_HEADER_ONLY)

#endif // ASIO_DETAIL_STRAND_EXECUTOR_SERVICE_HPP
